Graduated ND Filters

For over a year, I have liked my Canon T3i with my Canon EF-S 18-55mm, and also my Canon EF-S 55-250. I plan on upgrading to a 70D within the next year and also two more lenses. A Sigma 10-20 and also a Canon 100mm Macro Lense.

I am planning on buying Graduated Neutral Density Filters, but I am not sure which ones to go with. So far, I am looking at both Cokin and Hitech. I have heard of Lee, but they are super expensive.

A few questions I have are:

1) Is there any difference between Cokin and Hitech? Is one better than the other.

2) What is the difference between Hard and Soft Grad ND Filters? Is it better to have both just in case?

3) Should I also invest in a Reverse Grad ND Filter, are they worth it?

4) I was also thinking about buying a .6 and a .9 lense, but how often do people use a .3 or even a 1.2.

5) I have noticed that on the B&H Photo Website, they have some filters that are resin and others are not. What is the difference between a Resin filter and a non-resin Filter besides the price.

6) Since I will be using a Sigma 10-20 lense, I'm assuming that Filters that I will be buying in the future need to be bigger than 77mm, so I'm assuming a 100mm.

One last thing, It will be extremely helpful since I am new to Grad ND filters is for someone to post what the correct retanglular sizes (Grad ND Filter) I should be using for my 10-20mm since there are a variety of sizes.